The present disclosure relates to an illumination device having a light modulating element which expresses a scattering property or a transparency to light, and to a display device provided with the illumination device.
In association with recent rapid progress in higher image quality and better energy saving of a liquid crystal display, a method has been proposed, which realizes an improvement in a dark-place contrast by partially modulating an intensity of light of a backlight. This method mainly drives light-emitting diodes (LEDs), used as a light source of the backlight, partially to modulate the light of the backlight in accordance with a display image. Also, in view of an increasing demand for reduction in thickness for a large-sized liquid crystal display as in a small-sized liquid crystal display, an edge-light method has been a focus of attention, instead of a method which disposes a cold cathode fluorescent lamp (CCFL) or the LEDs immediately below a liquid crystal panel. The edge-light method disposes a light source at an edge of a light guide plate. In the edge-light method, however, it is difficult to perform partial driving, in which the light intensity of the light source is partially modulated.
As a technique for extracting light propagating in a light guide plate, Japanese Unexamined Patent Application Publication No. H06-347790 (JP-H06-347790A) proposes a display device utilizing a polymer-dispersed liquid crystal (PDLC), which switches between a transparent state and a scattering state, for example. This technique aims to prevent reflection and the like, and applies a voltage partially to the PDLC to switch over between the transparent state and the scattering state.
As for an edge-light backlight, there is a technology in which a printing pattern, a density of a geometry for the light extraction, or a size of a single pattern is varied in accordance with a distance from a light source (e.g., LEDs, a CCFL, and so forth) for a purpose of uniformizing an in-plane luminance, as disclosed in Japanese Unexamined Patent Application Publication No. H11-142843 (JP-H11-142843A), for example. A technology disclosed in JP-H11-142843A is, so to speak, a technology for extracting the light uniformly from the light guide plate, which technology only takes the extraction of light into consideration. As the technology of uniformizing the in-plane luminance besides JP-H11-142843A, there is a technology in which a light diffusion rate of a diffusion sheet is varied gradually in accordance with a distance from a light source, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-253335 (JP2004-253335A), for example.
It may be contemplated that the technology disclosed in JP-H11-142843A or that disclosed in JP2004-253335A may be combined with the PDLC disclosed in JP-H06-347790A to uniformize the in-plane luminance of light of the backlight. However, although this may allow the luminance to be uniformized, the luminance in dark displaying is increased. Thus, there is a problem in that a modulation ratio of bright displaying to the dark displaying is difficult to be made high.
It is desirable to provide an illumination device capable of uniformizing an in-plane luminance while increasing a modulation ratio, and a display device provided with the illumination device.